Preliminary Assessment of Modelling Issues Related to the Dynamics and Control of Graphite-Moderated MSRs

The Molten Salt Reactor (MSR) is one of the six innovative systems envisaged by the Generation IV International Forum for safe, proliferation resistant and sustainable nuclear energy production. The MSRs are characterized by a complex physical environment, as a consequence of the unusual role of the molten salt, which acts simultaneously as fuel and coolant. Such unique feature requires the development of dedicated simulation tools, able to take into account peculiar phenomena of Circulating Fuel Reactors (CFR) such as the delayed neutron precursor (DNP) drift and the subsequent decay out of the core. In this paper, reference is made to the Molten Salt Reactor Experiment (MSRE). The MSRE was an 8 MWth graphite-moderated MSR built at the Oak Ridge National Laboratory during the sixties. It represents a convenient validation framework due to the availability of both design and experimental data. The analysis is carried out by means of a dynamic model. All the main components of the experimental plant are simulated. The entire model is implemented in Simulink® (The MathWorks Inc., 2006). On the basis of the available MSRE experimental data, the proposed model results sufficiently accurate to predict the plant response in terms of the most relevant variables. In addition, the developed simulation tool is employed in order to assess some of the issues related to the control strategy of graphite-moderated MSRs. The analyses are carried out using the control toolbox provided by Simulink®. The dynamic response of the whole system is evaluated, and significant transient initiators are considered. Useful indications for transient behavior and possible control strategies are finally identified